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The suppression of MAD1 by AKT-mediated phosphorylation activates MAD1 target genes transcription

Chao-Kai Chou1, Dung-Fang Lee, Hui-Lung Sun

  • 1Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.

Molecular Carcinogenesis
|June 16, 2009
PubMed

Insights

AKT phosphorylation inhibits MAX dimerization protein 1 (MAD1) transcription suppression. This process, crucial in cancer cells, activates target gene transcription, promoting cell growth by altering MYC binding dynamics.

Area of Science:

  • Molecular Biology
  • Cancer Biology
  • Cell Signaling

Background:

  • MAX dimerization protein 1 (MAD1) suppresses transcription by competing with MYC for promoter binding sites, influencing cell proliferation and differentiation.
  • The regulation of MAD1, particularly in cancer cells, remains poorly understood.
  • MYC and MAD1 dynamics at gene promoters are critical for cellular processes.

Purpose of the Study:

  • To investigate the regulatory mechanism of MAD1 in cancer cells.
  • To elucidate the role of AKT signaling in modulating MAD1's transcriptional repressive function.
  • To understand how AKT-mediated phosphorylation affects MAD1's interaction with target gene promoters.

Main Methods:

  • Co-immunoprecipitation to demonstrate physical interaction between AKT and MAD1.
  • In vitro kinase assays to confirm AKT-mediated phosphorylation of MAD1.
  • Site-directed mutagenesis (S145A) to assess the role of phosphorylation.
  • Quantitative PCR and reporter assays to measure target gene transcription (hTERT, ODC).
  • Cell cycle analysis and cell proliferation assays.

Main Results:

  • AKT physically interacts with and phosphorylates MAD1.
  • Phosphorylation of MAD1 by AKT reduces its DNA-binding affinity, abolishing transcription repression.
  • Mutation of the phosphorylation site (S145A) abrogates AKT-mediated inhibition.
  • AKT promotes cell cycle progression and growth by inhibiting MAD1-mediated repression of target genes like hTERT and ODC.

Conclusions:

  • AKT-mediated phosphorylation of MAD1 is a key regulatory mechanism that inhibits its transcriptional suppressor activity.
  • This phosphorylation event releases the repression of MAD1 target genes, thereby promoting cell cycle progression and growth in cancer cells.
  • Targeting the AKT-MAD1 interaction could offer a novel therapeutic strategy in cancers where this pathway is dysregulated.

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